1. Field of the Invention
The present invention relates to a hydraulic control system for controlling a hydraulic actuator for a hydraulic excavator.
2. Description of the Related Art
According to a conventional method for performing a leveling work with use of a hydraulic excavator, a front end of a bucket is brought into contact with the ground while a boom and an arm are extended to a maximum and then boom raising operation and arm pulling operation are performed simultaneously to pull the bucket toward the excavator.
In the leveling work, when the arm assumes a nearly vertical attitude, a peripheral speed of the bucket front end becomes low relative to a cylinder speed of an arm cylinder, so there sometimes occurs a case where the cylinder speed of the arm cylinder is insufficient when the leveling efficiency is to be improved.
There is known a hydraulic excavator capable of solving the problem of delay in the boom speed which occurs upon simultaneous execution of the boom raising operation and the arm pulling operation (see, for example, Japanese Patent Laid-Open No. Hei 10-102547).
This known hydraulic excavator is configured in such a manner that the cylinder speed of a boom cylinder which is set for a fine operation taking the lifting work into account can be increased in the leveling work so as to permit operation at a speed matching a high arm speed.
In this hydraulic excavator, the boom whose speed is set for the fine operation can be actuated while allowing its speed to match the arm speed in the leveling work, but the excavator is not so configured as to permit an increase of the arm cylinder speed in the case where only the arm pulling operation is performed in the nearly vertical attitude of the arm.